Mitochondrial encephalomyopathies are a group of genetically heterogeneous disorders for which molecular diagnosis remains remarkably difficult. One particular form of mitochondrial encepaholmyopathy termed Leigh syndrome (LS) is a pediatric neurodegenerative condition and is a phenotypic manifestation of a variety of disorders of energy metabolism, most commonly cytochrome c oxidase (COX) deficiency. Because of locus heterogeneity associated with the clinical phenotype, identifying the molecular basis for this disease and other mitochondrial disorders remains an enormous challenge. Currently, the state-of-the-art in evaluating patients with suspected mitochondrial disorders is to perform a muscle biopsy and carry out biochemical assays of the respiratory chain. However, it does not provide a specific gene diagnosis, which remains a research endeavor. The investigators would like to explore the feasibility of establishing specific diagnoses using transcriptional profiling of total RNA from cultured skin fibroblasts. It is hypothesized that there will be unique transcriptional profiles for a number of single gene mitochondrial disorders. To apply this to LS and other mitochondrial diseases, data sets of known gene defects need to be developed. Preliminary data from the investigator's laboratory using COX deficient fibroblasts with mutations in SURF1 demonstrates that cluster analysis identifies subsets of genes that are either up or down regulated in a consistent fashion. The investigators propose to validate these observations using additional SURF1 deficient fibroblasts by comparing the output using three different software packages: Rosetta, GeneSpring, and dChip. Triplicate comparison will be made and compared to a single wild-type control also analyzed in triplicate. The effect of culture conditions and passage number will be examined. Clinically suspected samples will be analyzed and gene predictions made based upon known patterns. In those disorders manifested in cultured cells, this approach offers the potential for a much less invasive means of determining the specific nuclear gene defect. These results will help in counseling, the development of potential therapies, and assessing long-term outcomes.